Botanical Journal of the Linnean Society (2001), 135: 1—11. With 21 figures
doi:10.1006/bojl.2001.0417, available online at httpWwww.idealibrary.com on
IDE
Observations on the vegetative anatomy of
Austrobaileya: habital, organographic and
phylogenetic conclusions
SHERWIN CARLQUIST FLS
Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105, U.S.A.
Received December 1999; accepted for publication April 2000
For the single species of Austrobaileya (Austrobaileyaceae), quantitative and qualitative data are offered on the
basis of a mature stem and a root of moderate diameter. Data available hitherto have been based on stems of small
to moderate diameter, and roots have not previously been studied. Scanning electron microscope (SEM) photographs
are utilized for roots, and show compound starch grains. Roots lack sclerenchyma but have relatively narrow
vessels and abundant ray tissue. Recent phylogenies group Austrobaileyaceae with the woody families Illiciaceae,
Schisandraceae, and Trimeniaceae (these four may be considered Illiciales), and somewhat less closely with the
vesselless families Amborellaceae and Winteraceae and the aquatic families Cambombaceae and Nymphaeaceae.
The vessel-bearing woody families above share vessels with scalariform perforation plates; bordered bars on plates;
pit membrane remnants present in perforations; lateral wall pitting of vessels mostly alternate and opposite; tracheids
and/or septate fibre-tracheids present; axial parenchyma vasicentric (sometimes abaxial); rays Heterogeneous Type
I; ethereal oil cells present; stomata paracytic or variants of paracytic. Although comparisons between vesselbearing and vesselless families must depend on fewer features, Amborellaceae and Winteraceae have no features
incompatible with their inclusion in an expanded Illiciales.
© 2001 The Linnean Society of London
ADDITIONAL KEYWORDS: Amborellaceae ethereal oil cells Illiciaceae lianas
tracheid dimorphism Trimeniaceae vessel origin Winteraceae wood anatomy.
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INTRODUCTION
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Schisandraceae
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stomata
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considered by most authors to belong to Laurales (see
Metcalfe, 1987, for a survey). Several authors have
favoured a placement in Magnoliales (e.g. Endress,
1980). Loconte & Stevenson (1991) regarded Austro
baileyaceae as a sister group to the remainder of
Magnoliales. Some recent workers have grouped Au
strobaileya in or near Illiciales, along with Illiciaceae
and Schisandraceae (Nandi, Chase & Endress, 1998;
Renner, 1999). Trimeniaceae are included in this al
liance by Renner (1999); the Angiosperm Phylogeny
Group (1998), Nandi, Chase & Endress (1998), and
Renner (1999) also place Arnborellaceae, Ca
bombaceae, Nymphaeaceae, and Winteraceae close to
Illiciales. This group of families was left phylo
genetically unplaced and without an ordinal name by
the Angiosperm Phylogeny Group (1998). The pre
sentations of Nandi, Chase & Endress (1998) who call
the group “Magnoliid II” and Renner (1999), who calls
the group “expanded Nymphaeales”, clearly consider
this group of families as basal in dicotyledons and
therefore in angiosperms as a whole.
Vegetative anatomy of Austrobaileya scandens C. T.
White, sole species of Austrobaileyaceae, was first
studied by Bailey & Swamy (1949); their work has
been included in the summary of the family in Metcalfe
(1987). Although vegetative anatomy of the species is
relatively well known, important new details can be
added here because new kinds of material—liquidpreserved mature stems as well as roots of small to
moderate diameter—were available. New records for
anatomical feature character states in Austrobaileya
are offered below.
New information concerning Austrobaileya is of spe
cial interest because of the many primitive features
the genus has been claimed to possess (Bailey &
Swamy, 1949; Dickinson & Endress, 1983). New in
formation on Austmbaileya is also of potential value
because the phylogenetic position of the genus has
shifted considerably in recent years, depending on the
evidence adduced. Previous to 1980, Austrobaileya was
0024—4082/01/010001 + 11 $3500/0
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© 2001 The Linnean Society of London
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S. CARLQUIST
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Figures 1—4. Wood sections from mature stem of Austrobaileya scandens. Fig. 1. Transverse section; vessels increase
in diameter from near pith (below) to near cambium (above). Scale bar =100 tim. Fig. 2. TS. Axial parenchyma is
abaxial to vessels. Scale bar=50 am. Fig. 3. Tangential section; in additional to two wide multiseriate rays, less
conspicuous uniseriate rays are present. Scale bar = 100 urn. Fig. 4. Radial section; upright, square, and procumbent
cells are about equally abundant. Scale bar= 100 jam.
upright cells as sheathing and tip cells (Fig. 3). No
quantitative data for ray width and height are given
because of great variability in these features. Ray cell
walls are lignified; pits are commonly bordered as seen
in sectional view (Fig. 5). Starch is common in septate
fibre-tracheids, axial parenchyma and ray cells. Dark-
A USTROBAILEYA VEGETATIVE ANATOMY
5
ri.
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Figures 5—9. Sections of Austrobaileya sccindens. Figs 5—6. Mature stem secondary xylem radial section. Scale bar =
20 jim. Fig. 5. Portions of ray cells from radial section to show bordered nature of pits. Fig. 6. Fibre-tracheid with small
bordered pits and (above) a septum. Figs 7—9. TS medium-diameter root. Fig. 7. TS secondary xylem, pith below;
multiseriate ray very wide. Scale bar =100 jim. Fig. S. Portion of transection, secondary xylem (lower right) and
secondary phloem (upper right), with phloem ray (upper left) and xylem ray (lower left). Scale bar=50jim. Fig. 9.
Bark transection with phellem at top and secondary phloem below; sclerenchyma is absent. Scale bar =100 jim.
6
S. CARLQUIST
coloured phenolic compounds in some septate fibre
tracheids and in some ray cells (Fig. 4). No ethereal
oil cells were observed in stem secondary xylem.
Root wood anatomy
Growth rings absent (Fig. 7). Vessels mostly solitary,
mean number of vessels per group is 1.17. Vessels are
not in tangential or radial groupings. Mean vessel
diameter ranges from 18 un to 70 pm. Mean vessel
element length, 551 aim. All vessel elements have scal
ariform perforation plates (Figs 16—19). Bars of per
foration plates comparatively wide with respect to the
rather narrow perforations (Figs 16—19, especially Figs
17 and 19). Pit membrane remnants present in a few
perforations (Fig. 17). Number of bars per plate, 5—18;
mean number, 10.3. Mean vessel wall thickness,
2.2 pm. Mean number of vessels mm
2 was not de
termined because of abundance of ray tissue. Lateral
wall pitting of vessels is mainly alternate (Fig. 16),
although opposite, transitional, and scalariform pat
terns are occasional. Circular lateral vessel wall pits
are 7 jim in diameter. Imperforate tracheary elements
are tracheids and fibre-tracheids; septa are clearly
seen in at least some of the fibre-tracheids. Mean
tracheid length, 780 pm. Mean tracheid wall thickness,
5.2 pm. Tracheid pits are circular, pit cavity diameter
about 7 jim (Fig. 18, left). Apertures of the pits as seen
from the lumen side of the tracheid pits are slitlilce
(Fig. 20). Fibre-tracheids are often adjacent to rays.
Mean fibre-tracheid length, 763 jim. Fibre-tracheid
wall thickness, 0.9 jim (Fig. 21). Pits of fibre-tracheids
have narrow borders; pit cavity diameter is about 4 jim.
Septa in fibre-tracheids, where seen, consist of a thin
primary wall. Axial parenchyma vasicentric or abaxial,
in strands of two cells. Rays are uniseriate and narrow
to wide multiseriate; multiseriate rays tend to become
very wide toward the cambium, so that ray tissue is
more abundant than fascicular tissue in the secondary
xylem (Fig. 7). Ray cells are upright to square, rarely
procumbent, either with thin primary walls (Fig. 8,
left), or with moderately thin lignified walls. Scattered
ethereal oil cells are present in the multiseriate rays,
starch grains abundant in the septate fibre-tracheids
(Fig. 21), axial parenchyma, and rays. Deposits of
yellowish amorphous compounds are abundant in
early-formed vessels, occasional in other cells as drop
lets.
Stem cortex, bark, and phloem anatomy
The mature stem of Austrobaileya (Fig. 10) features
several layers of phellem, filled with dense ac
cumulations of dark phenolic compounds. There are
several layers of phelloderm, some cells of which con
tain phenolic compounds. Internal to the phelloderm
are large cortical cells. During expansion of the stem,
cortical cells are stretched tangentially, and some of
these cells are subdivided by a radial division. At the
inside of the cortex is a ring of sclerenchyma. The
sclerenchyma consists of strands of phloem fibres (cor
responding to fascicular areas of the primary stem)
between which brachysclereids are intercalated. As the
stem increases in diameter, the ring remains unbroken
because brachysclereids are continually added. In
ternal to the ring of selerenchyma is secondary phloem,
including dilated phloem rays. The phloem rays are
composed of thin-walled cells that contain abundant
compound starch grains. The axial secondary phloem
consists of nearly tangential bands of phloem par
enchyma alternating with bands of nonfunctional sieve
cells, except close to the cambium, where sieve cells
are still functional. Within the secondary phloem are
axially elongate idioblasts containing dark phenolic
compounds (Fig. 12). These idioblasts are in vertical
strands of one to three cells. Scalariform sieve areas
are conspicuous in radial sections of secondary phloem
(Fig. 13). No companion cells in the ordinarily accepted
sense of the term were observed in the material ex
amined (Fig. 11).
Root cortex, bark, and phloem anatomy
The outer surface of the root is clothed with layers of
phellem (Fig. 9); phellem cells are filled with deposits
of dark phenolic compounds which give the root a
brown colour in gross aspect. Internal to the phellem
and phellogen are several layers of phelloderm, most
of which lack deposits of phenolic compounds. Cortical
parenchyma cells and phloem ray cells with compound
starch grains. Parenchyma cells in both cortex and ray
regions are stretched tangentially and many of them
are subdivided by radial divisions (Figs 8, 9). There is
no sclerenchyma of any kind in the cortex or phloem.
Axial secondary phloem consists of phloem par
enchyma cells and sieve cells; no companion cells were
observed. In all but the youngest portions of the sec
ondary phloem, crushed sieve cells are intermixed with
persistent phloem parenchyma (Figs 8, 9). The phloem
ray cells have thin nonlignified walls. Ethereal oil cells
are present in phloem rays and cortex (Fig. 5, arrow).
Pitk anatomy
In the mature stem, pith cells are circular in transverse
section but when seen in longitudinal sections are
elongate, rectangular in outline. Pith cells decrease in
diameter toward the periphery of the pith (Fig. 1).
Many of the pith cells have horizontally-orientated
septa with thin primary walls only.
The root studied (Fig. 7) has a pith composed of
slender sclereids that are elongate as seen in lon
gitudinal section. No ethereal oil cells were observed
in pith of either the stem or the root.
A USTROBAILEYA VEGETATIVE ANATOMY
7
112
Figures 10—15. Sections of Austrobaileya scandens. Fig. 10. TS outer portion of mature stem, secondary xylem below,
bark above. Scale bar= 100 lam. Fig. 11. TS secondary phloem with portion of secondary xylem, below; no companion
cells evident. Scale bar = 20 jam. Fig. 12. Radial section from young stem with a little secondary growth; cells with dark
contents are elongate idioblasts containing phenolic compounds. Scale bar =100 am. Fig. 13. Sieve areas on sieve
element from radial section of mature stem. Scale bar = 20 tm. Figs 14, 15. Stomata and adjacent epidermal cells from
paradermal section of leaf. Scale bar = 201am. Fig. 14. Stoma with subsidiary cell above upper guard cell, subdivided
epidermal cells below. Fig. 15. Stoma with subdivided cell above upper guard cell; no other subsidiary cells definable.
8
S. CARLQUIST
Figures 16—21. SEM photographs of radial section of secondary xylem of medium-diameter root of Austrobaileya
scanclens. Fig. 16. Portions of two perforation plates; lateral wall pitting at upper left. Fig. 17. Four perforations, with
pit membrane remnants present in the central two. Fig. 18. Scalariform perforation plate at right; at left, tracheids
with outer surfaces exposed, showing circular pit membranes. Fig. 19. Vessel with narrow perforations, left; tracheid
at right. Fig. 20. Inner surface of tracheid, showing slitlike pit apertures. Fig. 20. Portions of fibre-tracheids filled with
compound starch grains. Magnification scale at lower right in each figure = 5 jim.
A USTROBAILEYA VEGETATIVE ANATOMY
Leaf anatomy and stomata
The observations on leaf anatomy offered by Bailey &
Swamy (1949) were confirmed in the present study.
The stomata of Austrobaileya have been reported to
be paracytic or anomocytic. That description is con
firmed by the present study. Two stomata are il
lustrated here. The stoma in Figure 14 would be
paracytic if there were a true subsidiary cell paralleling
the lower guard cell in the photograph. Instead, there
are two epidermal cells that appear to have cut off
derivatives that parallel the lower guard cell. Above
the guard cell pair in Figure 15 is a subsidiary cell that
has been subdivided. These stomata do not correspond
exactly to the concept of paracytic subsidiary cells
(or to the equivalent in other systems of stomatal
terminology), but could be considered intermediate
between paracytic and anomocytic.
DISCUSSION
Habit and organography
Correlations between habit and wood anatomy must be
examined before characters likely to reflect taxonomic
relationships can be identified. The data in Table 1
highlight wood modifications related to habit. Austro
baileya is a liana. The nature of wood with respect to
the lianoid habit in possibly related genera has been
examined in a series of papers that cover the three
other families of the revised order Illiciales. All species
of Schisandraceae are scandent, albeit variously, and
their wood has been studied by Cariquist (1999). Pip
tocalyx of the Trimeniaceae is a liana, and data on its
wood may be found in Carlquist (1984). All Illiciaceae
(Carlquist, 1982b) and the genus Trimenia Carlquist,
1984) of Trimeniaceae are shrubs or trees and have
wood patterns typical of nonscandent woody plants
and therefore offer good comparisons for study of wood
modifications of the scandent genera. The samplings of
woods of lianas by Carlquist (1975) show the following
characteristics for the lianoid species: vessels wider,
the stems beginning with narrower vessels but pro
ducing increasingly wider vessels as secondary growth
proceeds; (2) vessel density (number of vessels mm
2
of transection) relatively great when one takes the
wide vessel diameter into account; (3) vessel elements
shorter; (4) in those families with scalariform per
foration plates (e.g. Dilleniaceae, in which Tetracera
is scandent), fewer bars per perforation plate. The
vessel elements of Austrobaileya may not seem short,
but when compared to those of Illicium, they are
shorter. Length of vessel elements in scandent species
may not represent the scandent habit per se, but may
be related to the degree of phylogenetic specialization
of the scandent genus, since more specialized dicotyledons tend to have shorter vessel elements (Bailey
9
& Tupper, 1918). Another possible factor in this regard
is that scandent species accumulate secondary xylem
relatively slowly, and thus may exhibit a more juvenile
wood; in typical woody species, length of vessel ele
ments increases with amount of secondary growth
(Bailey & Tupper, 1918).
The differences between stem wood and root wood
of Austrobaileya may be explained by function: the
roots evidently serve more for storage (judging from
abundance of ray tissue and abundance of starch), the
stems more for water conduction. Thus, the root vessels
of Austrobaileya are narrower than those of the stem,
which runs contrary to the generalization of Patel
(1965) that within a give species, root vessels are wider
than those of stem. The narrowness of perforations in
perforation plates of roots of Austrobaileya may also
be also indicate that the root structure is less adapted
to meet high conductive rates of water in comparison
to the stem, in which perforations are relatively wide
and bars comparatively thin.
There are ethereal oil cells in the cortex and phloem
rays of the root in Austrobaileya, whereas ethereal oil
cells have not been reported in comparable tissues of
the stem (Table 1). Perhaps the abundance of starch
storage in the root and the presence in the soil of starchconsuming pathogens provide reasons for a selective
value of ethereal oil cells in the root. Likewise, the
dark-coloured phenolics in phellem of the root may
deter predation or entry of pathogens. Ethereal oil
cells are present in wood of Schisandraceae (Table 1),
but not in wood of Illiciaceae. Mucilage cells, a sort of
close vicarious equivalent to oil cells, are present in
fibre-like axial xylem cells of Trimenia and in ray cells
of Piptocalyx. The lack of oil cells in Illicium wood is
not a significant taxonomic character; oil cells are
located elsewhere in the plant in Illicium (Table 1).
Idioblasts (crystals, laticifers, etc.) are always more
common closer to the surface of a plant, and are least
common in wood (deposition of deterrent compounds
in the lumina of dead heartwood cells forms a barrier
to rot or predation equivalent to the idioblasts near
the plant surface).
Phylogeny
Austrobaileyaceae are grouped with the vessel-bearing
families Illiciaceae, Schisandraceae, and Trimeniaceae
into an order that could be called an expanded version
of Illiciales, by the Angiosperm Phylogeny Group
(1998), and other recent authors (see Introduction).
Features that link Austrobaileyaceae, Illiciaceae, Schi
sandraceae, and Trimeniaceae with respect to wood
anatomy are (Table 1): vessels with scalariform per
foration plants (chiefly with more than 10 bars);
bordered bars on perforation plates; pit membrane
remnants in perforation (see Cariquist, 1992); vessels
10
S. CARLQUIST
with mostly alternate or opporsite lateral wall pits;
tracheids with large circular bordered pits (both
tracheids and septate fibre-tracheids in Austro
baileyaceae; septate fibre-tracheids and no tracheids in
Trimeniaceae); vasicentric axial parenchyma (tending
towards abaxial in Austrobaileyaceae and Sch
isandraceae, some diffuse parenchyma in Illiciaceae);
rays corresponding to Heterogeneous Type I of Kribs
(1935); and ethereal oil cells or mucilage cells (see
comments in above paragraph). This is a surprising
list of shared features, and all of them except for the
presence of septate fibre-tracheids are best interpreted
as primitive character states (plesiomorphies). The
development of fibre-tracheids in Austrobaileya has
been interpreted as an apomorphy here. The ray type
in all four families is the same. The scalariform endwall pitting of tracheids in Amborella (Metcalfe, 1987)
may be a precursor to development of vessels with
scalariform perforation plates, as in Austrobaileya and
Illiciaceae.
A striking feature of considerable phylogenetic sig
nificance is the presence of porose pit membrane rem
nants in Austmbaileya, Illiciaceae (Carlquist, 1992)
and Schisandraceae (Carlquist, 1999). Trimeniaceae
have not been studied in this respect. The porose pit
membrane remnants seem just a small step beyond
the porose pit membrane (presumably intact) of tra
cheids of Bubbia (Carlquist, 1983).
The lack of companion cells in Austrubaileya claimed
by Bailey & Swamy (1949) was essentially confirmed by
Huber & Graf (1955), who found only a few companion
cells. No companion cells were identified in the present
study. Srivastava (1970) claimed that Austrobaileya
has companion cells but he used an altered definition
of that terms. Companion cells have traditionally been
considered sister cells of sieve-tube elements, but Sri
vastava (1970) considers cells that are not sister cells
of the sieve elements to be companion cells. This par
allels a similar departure from the traditional defin
ition in Gnetum (Martens, 1971). The radial files of
slender parenchyma cells alternating with sieve cells
in Gnetum have been rejected as companion cells by
most (but not all) authors (Martens, 1971). Austro
baileya differs from Illiciaceae, Schisandraceae, and
Trimeniaceae in having a paucity of companion cells,
if the observations of Huber & Graf (1955) are correct,
but this is a difference of degree rather than a character
state difference, since companion cells are more abund
ant in the three families named (Melcalfe, 1987).
Features of bark of Austrobaileya other than oc
currence of companion cells are compatible with what
is known about the bark of Illiciales sensu lato (see
Metcalfe, 1987).
Nodes are unilacunar in all four families (Table 1),
with deviations only in trace number: two in Sch
isandraceae (three traces) and one in Illicium.
Stomata are paracytic or possibly some related type
in the woody families of the expanded Illiciales except
for Austrobaileya (which has mixed anamocytic and
paracytic) Illiciaceae (paracytic and laterocytic) and
Schisandraceae (haplocheilic) according to Metcalfe
(1987). In the haplocheilic type, the subsidiary cells
are cut from adjacent epidermal cells rather than from
the mother cell of the guard cell, and some stomata in
Austrobaileya may correspond to an incipient haplo
cheilic type. More study of ontogeny of stomata, with
appropriate terminological corrections, is needed.
Chloranthaceae are said to have “paracytic variants”
in stomata of leaves (Metcalfe, 1987), and this term
might be applied to Austrobaileya and Schisandraceae
as well.
Thus, vegetative anatomy as a whole supports the
concept of an expanded Illiciales. The differences other
than those related to habit are relatively minor, and
the degree of identity or close identity in wood and
other vegetative features (Table 1) is greater than one
might expect for a group of relatively ancient families of
dicotyledons. If, as recent molecular evidence suggests,
Nymphaeales are basal to Illiciales, the anatomy of
Nymphaeales is very difficult to compare to that of
Illiciales because so many of the differences between
the two orders are attributable to the aquatic (or near
aquatic, Barclaya) habit of Nymphaeales.
REFERENCES
Angiosperm Phylogeny Group. 1998. An ordinal clas
sification for the families of flowering plants. Annals of the
Missouri Botanical Garden 85: 531—553.
Bailey 1W, Swamy BGL. 1949. The morphology and re
lationships of Austrobaileya. Journal of the Arnold Ar
boretum 30: 211—226.
Bailey 1W, Tupper WW. 1918. Size variation in tracheary
cells. I. A comparison between the secondary xylems of
vascular cryptogams, gymnosperms, and angiosperms. Pro
ceedings of the American Academy of Arts and Sciences 54:
149—204.
Carlquist S. 1975. Ecological strategies of xylem evolution.
Berkeley & Los Angeles: University of California Press.
Cariquist S. 1982a. The use of ethylene diamine in softening
hard plant structures for paraffin sectioning. Stain Tech
nology 57: 311—317.
Cariquist S. 1982b. Wood anatomy of Illicium (Illiciaceae):
phylogenetic, ecological, and functional interpretations.
American Journal of Botany 69: 1587—1598.
Cariquist S. 1984. Wood anatomy of Trimeniaceae. Plant
Systematics and Evolution 144: 103—118.
Carlquist S. 1988. Tracheid dimorphism: a new pathway
in evolution of imperforate tracheary elements. Aliso 12:
103—118.
Carlquist S. 1992. Pit membrane remnants in perforation
plates of primitive dicotyledons and their significance.
American Journal of Botany 79: 660—672.
AUSTROBAJLEYA VEGETATIVE ANATOMY
Carlquist S. 1999. Wood and bark anatomy of Sch
isandraceae: implications for phylogeny, habit, and vessel
evolution. Aliso 18: 45—55.
Dickison WC, Endress PK. 1983. Ontogeny of the stemnode continuum of Austrobaileya. American Journal of
Botany 70: 906—911.
Endress PK. 1980. The reproductive structures and sys
tematic position of the Austrobaileyaceae. Botanisches
Jahrbücher 101: 393—433.
Huber B, Graf E. 1955. Vergleichende Untersuchungen uber
die Geleitzellen der Siebrohren. Berichte der deutschen
botanischen Gesellschaft 68: 303—310.
IAWA Committee on Nomenclature. 1964. Multilingual
glossary of terms used in wood anatomy. Winterthur: Kon
kordia.
Kribs DA. 1935. Salient lines of specialization in the wood
rays of dicotyledons. Botanical Gazette 96: 547—557.
Loconte H, Stevenson DW. 1991. Cladistics of the Mag
noliidae. Cladistics 7: 267—296.
Martens P. 1971. Les Gnëtophytes. Handbuch der Pflan
zenanatomie Spezieller Teil, Band XII, Teil 2. Berlin &
Stuttgart: Gebruder Borntraeger.
Mathews S, Donoghue MJ. 1999. The root of angiosperm
phylogeny inferred from duplicate phytochrome genes. Sci
ence 286: 947—950.
Metcalfe CR. 1987. Anatomy of the dicotyledons. Ed. 2,
Volume III. Magnoliales, Illiciales, and Laurales. Oxford:
Clarendon Press.
11
Nandi 01, Chase MW, Endress PK. 1998. A combined
cladistic analysis of angiosperms using rbcL and non-mo
lecular data. Annals of the Missouri Botanical Garden 85:
137—212.
Parkinson CL, Adams KL, Palmer JD. 1999. Multigene
analyses identify the three earliest lineages of extant
flowering plants. Current Biology 9: 1485—1488.
Patel RN. 1965. A comparison of the anatomy of the
secondary xylem in roots and stems. Holzforschung 19:
72—79.
Qui Y-L, Chase M, Les DH, Hills HG, Parks CR. 1993.
Molecular phylogenetics of the Magnoliidae: a cladistic
analysis of nucleotide sequences of the plastid gene rbcL.
Annals of the Missouri Botanical Garden 80: 587—606.
Qui Y-L, Lee J, Bernasconi-Quadroni F, Soltis DE,
Soltis PS, Zanis M, Zimmer EA, Chen Z, Savolainen
V, Chase MW. 1999. The earliest angiosperms: evidence
from mitochondrial and nuclear genomes. Nature 402:
404—407.
Henner SS. 1999. Circumscription and phylogeny of the
Laurales: evidence from molecular and morphological data.
American Journal of Botany 86: 1303—1315.
Soltis PS, Soltis DE, Chase MW. 1999. Angiosperm phylo
geny inferred from multiple genes as a tool for comparative
biology. Nature 402: 402—404.
Srivastava LM. 1970. The secondary phloem of Au
strobaileya scandens. Canadian Journal ofBotany 48:341—
359.